1. Field of the Invention
Generally, the present invention relates to the construction of a seal that is mounted on a bearing unit for an automotive vehicle wheel that includes two elements, such as inner race and outer race, which rotate relative to each other. More particularly, the present invention related to such seal construction that includes an encoder that is intended for use in detecting the number of revolutions for each of the four automotive vehicle wheels, such as front and rear, right and left wheels that are under control of the antilock brake system (ABS) or traction control system (TCS).
2. Prior Art
There is a conventional apparatus for detecting the number of revolutions for the automotive vehicle wheel that is often used in conjunction with the antilock/skid control system to prevent any lock or skid from occurring on the automotive vehicle wheels. This apparatus includes an encoder that responds to the vehicle wheel or its bearing unit that is rotating and produces pulses magnetically that represent the number of revolution for the vehicle wheel or its bearing unit, and a sensor that is disposed to face opposite the encoder for responding to the pulses from the encoder.
Usually, the conventional apparatus for detecting the number of wheel revolutions is disposed in conjunction with the sealing device that is capable of sealing the bearing unit for the wheel, and is developed as an encoder-equipped seal that provides both the sealing function and rotation detecting function that is implemented as the encoder. The apparatus is used for the practical purposes. An example of the apparatus is disclosed in Japanese patent application as published under No. H6 (1994)-2810118.
One typical example of such conventional encoder equipped seal is now described by referring to FIG. 8. As shown in FIG. 8, the conventional encoder-equipped seal includes a reinforcing ring 102 having a cylindrical portion 102a extending in the axial direction of the bearing and a flanged portion 102b extending radially from the cylindrical portion 102a, a magnetic ring 103 attached to the flanged portion 102b, and a seal lip 104 disposed in the radial circumferential edge of the flanged portion 102b. 
The reinforcing ring 102 is made of any of the metals such as iron, stainless steel and the like.
The seal lip 104 is an elastic element made of any of the elastic materials such as synthetic rubber, synthetic resin and the like, and molded into the appropriate shape by using any of the processes, such as the vulcanized bond molding process, so that it is supported by the flanged portion 102b of the reinforcing ring 102.
The magnetic ring 103 is an annular multi-pole magnet having S polarity and N polarity magnetized alternately in the circumferential direction, and acts as the encoder that produces pulses magnetically.
The magnetic ring 103 can be made as follows.
Firstly, an annular ring is molded by pressure-molding, a mixture composed of any of ferromagnetic materials, such as any of quench-hardened molding materials, deposit-hardened molding materials or sintered materials, in powdery or granule forms, for example, hard ferrite in powdery or granule forms, and any elastic element such as synthetic rubber or synthetic resin. The annular ring thus obtained is united with the reinforcing ring 102 by bonding it to the outer lateral side of the flanged portion 102b (right side in FIG. 8, and that is outer lateral side of the bearing unit). The annular ring thus united with the reinforcing ring 102 is magnetized so that it has S polarity and N polarity magnetized alternately in the circumferential direction. Thereby, a magnetic ring 103, which is an annular multi-pole magnet having S polarity and N polarity magnetized alternately in the circumferential direction, united with the reinforcing ring 102, and acts as the encoder, is obtained.
Alternatively, the magnetic ring 103 can be made as follows.
The reinforcing ring 102, which has the preliminary foundation treatment and adhesive coating on the axial outer lateral side of its flanged portion 102b, is placed into a mold together with the mixture composed of any of the above-mentioned ferromagnetic materials and any of the above-mentioned elastic elements, where they are pressed under the applied heating so that they can be bonded together by the vulcanized bonding process. The result thus obtained includes an annular ring united with the reinforcing ring 102 by vulcanized bonding to the outer lateral side of the flanged portion 102b (right side in FIG. 8, and that is outer side of the bearing unit). The annular ring thus united with the reinforcing ring 102 is magnetized so that it has S polarity and N polarity magnetized alternately in the circumferential direction. Thereby, a magnetic ring 103, which is an annular multi-pole magnet having S polarity and N polarity magnetized alternately in the circumferential direction, united with the reinforcing ring 102, and acts as the encoder, is obtained.
As shown in FIG. 8, this encoder-equipped seal is used in conjunction with the wheel bearing unit including two elements, such as outer race 105a and inner race 105b, rotating relative to each other. In the embodiment shown in FIG. 8, it is assumed that the outer race 105a corresponds to the rotational element and the inner race 105b corresponds to the non-rotational element.
The interior of the wheel bearing unit can be isolated from the outside by allowing the seal lip 104 to make sliding contact with the circumferential surface of the inner race 105b. In this way, the bearing unit can be protected against the entry of water or foreign matter from the outside.
In this encoder-quipped seal, a sensor 106 that has the form shown in FIG. 1(c) may be disposed in close proximity of the magnetic ring 103 so that the sensor can face opposite the magnetic ring 103. Then, the magnetic ring 103 produces pulses magnetically that represent the number of wheel revolutions and the sensor 106 responds to the pulses. Thus, the number of wheel revolutions can be detected through the sensor 106.
In the conventional encoder-equipped seal such as the one described above, it may be understood from the above description that the magnetic ring 103 is made of the mixture composed of any of the ferromagnetic materials and any of the elastic materials, and the seal lip 104 is only made of any of the elastic elements. Thus, the magnetic ring 103 and seal lip 104 are based on the respective materials having the different properties, and are provided on the reinforcing ring 102 by using any respective appropriate bonding method. This means that the magnetic ring 103 and seal lip 104 must be formed by following the two different steps as described below.
The first step is to provide a seal lip 104 formed from any synthetic rubber or synthetic resin on the flanged portion 102b of the reinforcing ring 102 by using any vulcanized bonding method so that the seal lip 104 is supported by the flanged portion 102b. The second steps is to attach a magnetic ring 103 formed from the mixture of any ferromagnetic material such as hard ferrite and any elastic material to the flanged portion 102b of the reinforcing ring 102.
The second step of attaching the magnetic ring 103, which is formed from the mixture of any ferromagnetic material such as hard ferrite and any elastic material, to the flanged portion 102b of the reinforcing ring 102 can be performed in any one of the following two ways, for example, as the before described.
In the first way, this second step includes the step of molding the mixture of the ferromagnetic material and elastic material under the applied pressure into the annular shape and then bonding the resulting annular shape to the flanged portion 102b of the reinforcing ring 102, as described above.
In the second way, this second step includes the steps of providing a reinforcing ring 102 including a flanged portion 102b having the preliminary foundation treatment and adhesive coating thereon, and then placing the reinforcing ring 102 together with the mixture of the ferromagnetic material and elastic material into a mold, where they are molded under the applied heating by the vulcanized bonding method.
Although the first way is advantageous in making the molding easier but is disadvantageous in that the additional steps such as adhesive coating or heated bonding are involved. Another disadvantage is the low mounting precision (eccentricity).
The second way is not desirable because it involves the use of different materials that require the different vulcanization periods of time or temperatures, which makes it difficult to use a general compression molding process. It is important to measure the quantities of materials to be used accurately. Thus, the second way is not desirable because it only permits the molding process to occur within the very narrow allowance.
For the recent years, the injection molding process is used in order to avoid the problems mentioned above. The injection molding process permits the molding to occur although the different materials have the different vulcanization periods of time, allowing the quantities of materials to be determined by controlling them by the injection pressures. However it requires the expensive molds or molding machines as well as the high-level molding technology. For this reason, the injection molding process is not popular.